A fluorene derivative is excellent in heat resistance and transparency, and therefore, recently, shows promise as a material for production of a polymer with high index of refraction (e.g., epoxy resin, polyester, polyether, and polycarbonate). The fluorene derivative shows promise as a raw material of an optical lens, film, plastic optical fiber, optical disc substrate, heat-resistant resin, and engineering plastic etc.
As a method for producing a fluorene derivative, there is disclosed a method for obtaining 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene by reacting fluorenone with 2-phenoxyethanol by using sulfuric acid and a thiol serving as catalysts, which method includes (a) adding a lower aliphatic alcohol to a reaction liquid to dissolve a target substance and thereafter (b) adding water to precipitate and recover the target substance (refer to Patent Literature 1).
Further, there is disclosed a method of recovering phenoxyethanol by (a) recovering precipitated 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene by filtration, (b) removing a lower aliphatic alcohol from a filtrate by distillation, and (c) adding water to a liquid remaining in a pot to separate a phenoxyethanol layer (refer to Patent Literature 2).
However, since this method uses a large amount of sulfuric acid, the sulfuric acid or sulfur component derived from the catalysts is mixed in obtained crystals. This causes problems such as coloration of finished products, reduction in purity, and reduction in stability. Further, in order to obtain high-purity finished products such as optical resin materials, it is necessary to repeat purification to remove sulfur. In addition, it is necessary to carry out complex operations so as to recover phenoxyethanol from the filtrate.
As methods for solving such problems, there are disclosed (a) a method of: adding, to a reaction solution obtained by reacting fluorenone with phenoxyethanol by using sulfuric acid and a thiol serving as catalysts, water and a solvent incompatible with water; and recovering 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene from an organic phase (refer to Patent Literatures 3 and 4) and (b) a method of treating, with ion exchange resin, an organic phase containing 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene (refer to Patent Literature 5). However, sulfur still remains in both methods. Therefore, the methods have not completely solved the problems such as deteriorations in hue and purity of finished products.
Further, there is disclosed a method of (a) reacting fluorenone with phenoxyethanol by using sulfuric acid and a thiol serving as catalysts, (b) adding an alkaline aqueous solution to an obtained acid reaction liquid, and thereafter (c) coprecipitating 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene, i.e., target substance, and sulfate and (d) recovering a coprecipitated product by filtration (Patent Literature 6). However, according to this method, in order to separate the 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene and sulfate contained in the coprecipitated product thus recovered by filtration, the target substance is partitioned into an organic phase by redissolving the coprecipitated product with an extract agent and thereafter the 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene is recovered by crystallization and filtration. That is, it is necessary to carry out industrially complex filtration and recovery operations two or more times.
As a method using no sulfuric acid, there is disclosed a method that uses metal exchange type montmorillonite (refer to Patent Literature 7). However, according to this method, montmorillonite to be used is extremely expensive and is difficult to obtain in large amounts. Further, according to this method, it is necessary to produce a metal-substituted montmorillonite catalyst by reacting commercially available montmorillonite with a metal chloride. Moreover, since a thiol such as beta-mercaptopropionic acid serving as a promoter is used for the purpose of increasing reaction yield, sulfur is to be mixed in the finished products. Therefore, in order to obtain high-purity finished products, it is necessary to repeat purification so as to remove sulfur.
Further, the inventors of the present invention disclose, as a method using no sulfuric acid, a method of obtaining 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene by reacting fluorenone with phenoxyethanol in the presence of a heteropoly acid serving as a catalyst, which method includes (a) partitioning a target substance into an organic phase by adding an extract agent constituted by water and an organic solvent to a reaction liquid and (b) recovering the target substance (refer to Patent Literature 8). Further, the inventors of the present invention propose: a method for producing 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene from fluorenone and 2-phenoxyethanol in the presence of a heteropoly acid catalyst (Patent Literature 9); and a method for producing 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene whose melting point is 160° C. to 166° C. (Patent Literature 10). Moreover, there is disclosed a method of obtaining a fluorene derivative by reacting fluorenone with a phenol by using hydrochloric acid and a thiol serving as catalysts, which method includes partitioning a target substance into an organic phase by using an extract agent and recovering the target substance (refer to Patent Literature 11). However, according to these methods, a reaction liquid contains a large amount of unreacted phenol or phenoxyalcohol, which is highly soluble in water. This may cause a reduction in liquid separability, and thus cause a deterioration in hue or purity. Further, these methods place a large burden on the environment, because a large amount of organic compounds such as phenols or phenoxyalcohols are mixed in an aqueous phase, and/or it is necessary to use a large amount of organic solvent for liquid separation. Therefore, these methods are not industrially advantageous.
Furthermore, there is disclosed a method of reacting fluorenone with phenoxyethanol in the presence of cation exchange resin, while carrying out dehydration so that water content of a liquid phase of the reaction system is 0.1 wt % or less (Patent Literature 12). Patent Literature 12 states that it is possible to isolate a high-purity fluorenone derivative even by a general-purpose method. However, with this method, it is necessary to control water content of the reaction liquid. The control of the water content becomes more difficult and complex as the scale of the reaction increases. Further, this may reduce yield or purity. In addition, according to the study carried out by the inventors of the present invention, it is necessary to use strongly acidic ion exchange resin having a sulfonic acid group in order to cause reaction to proceed effectively. Due to impurities to be eluted from the ion exchange resin, a mere combination of general-purpose purifying operations may not be capable of achieving hue and purity that are required for materials for optical use.
Further, as described earlier, in recent years, a fluorene derivative such as 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene has been used as a raw material of for example optical polycarbonate resin. For such use, it is required more than ever to produce, at high yield and at low cost, non-colored and high-purity finished products that contain no reaction by-products and no sulfur component.
Generally, in order to obtain a high-purity finished product by reacting fluorenone with a phenoxyalcohol or a phenol, it is required to reduce by-products in a reaction process. Other ways to reduce by-products to some extend include a process of neutralizing an obtained reaction mixture and a process of purifying an obtained product. Further, various conditions in the process of neutralizing the obtained reaction mixture and the process of purifying the obtained product are important for obtaining an non-colored finished product.
Usually, by-products are less generated as a reaction temperature decreases. Note, however, that a rate of reaction is inevitably reduced. Further, although the process of neutralizing the obtained reaction mixture and the process of purifying the obtained product would achieve improvement in purity of finished products and reduction in by-products and suppression of coloration, the yield of the finished products may decrease. Therefore, in order to obtain non-colored high-purity finished products at high yield, it is important to optimally combine the processes having optimum operation conditions throughout the entire production process. Under such circumstances, it is strongly desired to find such an optimum production method.